In recent years, there has been an increasing demand for concentration measurement devices of the type, which makes nitrogen monoxide, etc., in a sample gas undergo a chemical reaction with ozone or other oxidizing gas and measures the concentration of the nitrogen monoxide, etc., in the sample gas based on the intensity of the light due to chemiluminescence resulting from the reaction. With such a device, it is possible, for example, to measure the concentration of nitrogen monoxide in the expired air of an asthmatic patient in order to monitor the effects of treatment, and to measure the concentration of nitrogen monoxide in the exhaust gas of an automobile in order to tackle environmental problems.
Such a concentration measurement device requires a luminescent reaction measurement device that measures the intensity of the light due to chemiluminescence, and a luminescent reaction measurement device, such as that disclosed in Japanese Unexamined Patent Publication (Tokukai) No. Hei 7-333150, is popularly used. This device is equipped with a reaction tank, having an indented part formed therein, and a photodiode, having a light receiving surface and serving as a light detector, and this photodiode is fitted into the indented part of the reaction tank so that a reaction chamber of a predetermined space is formed by the light receiving surface and the inner surface of the indented part of the reaction tank.
With this luminescent reaction measurement device, for example, nitrogen monoxide is made to react with ozone in the reaction chamber, the intensity of the light resulting from chemiluminescence is detected by the light receiving surface of the photodiode and an electrical signal according the detection is output.